The present invention concerns a subsurface safety valve for controlling the flow of well fluids, particularly oil and/or gas fluids produced from subsurface formations.
The valve of this invention does not require the additional tubings or pipes which are required to supply fluid from the surface in hydraulic surface controlled safety valve systems and thereby overcomes the inherent disadvantages of such safety valve systems. Also, this valve provides an improvement over safety valves which are operated solely by velocity and safety valves which are operated solely by changes in absolute tubing pressures. It combines the differential pressure feature of the velocity valve and the feature of change in the absolute tubing pressure. By employing different piston areas this valve eliminates springs and spacers used in velocity-type valves. It also eliminates pre-charged chambers used in pressure actuated valves.